seawall n : a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away [syn: breakwater, groin, groyne, mole, bulwark, jetty]

English

Etymology

sea + wall

Noun

1. a coastal defence in the form of an embankment

See also

• breakwater
• groyne

Translations

• ttbc Spanish: muro'n de mar (the apostrophe represents a missing accent)

A seawall is a form of hard coastal defence constructed on the inland part of a coast to reduce the effects of strong waves and are built in the water.

In Britain, "sea wall" also means an earth bank used to create a polder – a dike. Seawalls may be constructed from a variety of materials: most commonly, they are constructed of reinforced concrete, boulders, steel, or wire cages filled with pebbles. Additional seawall construction materials include: vinyl, wood, aluminum and fiberglass composite. Poorly designed seawalls require constant maintenance, as the waves can constantly attack the base of the seawall. Seawalls can be expensive to build, costing between £4000 to £7000 per metre. Modern concrete sea walls tend to be curved to deflect the wave energy back out to sea, reducing the force.

Design principles and types

A range of seawall types can be envisaged in relation to wave energy, resembling cliff and beach profiles. Vertical seawalls are built in particularly exposed situations. These reflect wave energy and under storm conditions standing waves (clapotis) will develop. In some cases piles are placed in front of the wall to lessen wave energy slightly. Curved or stepped seawalls are designed to enable waves to break and to dissipate wave energy. The curve can also prevent the wave overtopping the wall, and provide additional protection for the toe of the wall.

A series of rubble mound-type structures (or revetments, riprap) are used in lesser energy settings. The least exposed sites involve the lowest-cost technology, bulkheads or revetments of sand bags or geotextiles. These serve to armour the shore and impede erosion. They may be either watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.

History

Pondicherry

On December 26, 2004, when towering waves of the 2004 Indian Ocean earthquake crashed against India's south-eastern coastline killing thousands, the former French colonial enclave of Pondicherry (now Puducherry) escaped unscathed. During the city's nearly three centuries as a French colony, French engineers had constructed and maintained a massive stone seawall, which kept Pondicherry's historic center dry even though tsunami waves drove water 24 feet above the normal high-tide mark.

The barrier was initially completed in 1735. Over the years, the French continued to fortify the wall, piling huge boulders along its 1.25-mile (2-kilometer) coastline to stop erosion from the waves pounding the harbour. At its highest, the barrier running along the water's edge reaches about 27 feet above sea level. The boulders, some weighing up to a ton, are weathered black and brown. The sea wall is inspected every year. Whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong.

The Union Territory of Pondicherry recorded some 600 deaths from the huge tsunami waves that struck India's coast after the mammoth underwater earthquake (which measured 9.0 on the moment magnitude scale) off Indonesia, but most of those killed were fishermen who lived in villages beyond the artifical barrier.

See also

• Retaining wall
• Accropode
• Dike
• Alaskan Way Seawall
• Galveston Seawall
• Georgetown Seawall
• Gold Coast Seawall
• Saemangeum Seawall
• Vancouver Seawall

References

• De Centre d'études maritimes et fluviales. (2007). Rock Manual. The use of rock in hydraulic engineering. Ciria. ISBN 0860176835.
• N.W.H. Allsop. (2002). Breakwaters, coastal structures and coastlines.Thomas Telford. ISBN 0727730428.

External links

• Channel Coastal Observatory - Seawalls
• Constructing a new sea wall and defences at Lyme Regis in Dorset

Gallery

image:seawallbembr.jpg|Seawall in Bembridge, UK image:Sicilia1.jpg|Seawall in Sicily image:Poland-seawall.jpg|Seawall in Poland‎

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